Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

The invention addresses the problem of providing a polyimide precursor, a
polyimide precursor solution, and a mixture slurry, each capable of more
firmly binding active material particles to a current collecting body.
The polyimide precursor solution according to the invention contains a
tetracarboxylic acid ester compound, a diamine compound having an anionic
group, and a solvent. The solvent dissolves the tetracarboxylic acid
ester compound and the diamine compound. As the tetracarboxylic acid
ester compound, a 3,3',4,4'-benzophenonetetracarboxylic acid diester is
particularly preferred. Examples of the "diamine compound having an
anionic group" include 3,4-diaminobenzoic acid, 3,5-diaminobenzoic acid,
and m-phenylenediamine-4-sulfonic acid. Further, the mixture slurry
according to the invention contains active material particles in the
polyimide precursor solution.

Claims:

1. A polyimide precursor solution comprising: a tetracarboxylic acid
ester compound, a diamine compound having anionic groups, and a solvent
that dissolves the tetracarboxylic acid ester compound and the diamine
compound.

29. An electrode comprising: a current collector body, and an active
substance layer obtained from the mixture slurry as recited in claim 28
and being on the current collector body.

30. An electrode comprising a current collector body, and an active
substance layer having active substance particles and a polyimide resin
that along with mutually binding together the active substance particles
also binds together the current collector body and the active substance
particles, the active substance layer being on the current collector
body, the polyimide resin having anionic groups.

Description:

TECHNICAL FIELD

[0001] The present invention relates to polyimide precursor solutions and
polyimide precursors. In addition, the present invention relates to
polyimide resins obtained from polyimide precursor solutions or polyimide
precursors. Furthermore, the present invention relates to mixture
slurries that contain active substance particles in a polyimide precursor
solution, particularly mixture slurries for use in forming an anode.
Additionally, the present invention relates to methods for producing
these mixture slurries. In addition, the present invention relates to
electrodes (anodes) obtained from these mixture slurries. Furthermore,
the present invention relates to methods for forming these electrodes.

BACKGROUND ART

[0002] In the past, "the use of a monomeric polyimide precursor as a
binder added to the anode mixture slurry that forms the anode for lithium
ion secondary batteries and the like" was proposed (for example, see:
Japanese published unexamined patent application no. 2008-034352, etc.).
This monomeric polyimide precursor comprises mainly a tetracarboxylic
acid ester compound and a diamine compound that, for example, upon
heating forms a porous structure by undergoing high-molecular-weight
polymerization via imidization. By undergoing high-molecular-weight
polymerization, the monomeric polyimide precursor becomes firmly bound to
the active substance particles and current collector body, and adding
this monomeric polyimide precursor to an anode mixture slurry can
adequately prevent the loosening and detachment of the active substance
layer from the anode current collector body due to expansion and
contraction of the active substance particles. Furthermore, by forming a
porous structure, a solid template (mold) is formed that encloses the
active substance, and when the active substance particles bind strongly
in the boreholes, the porous structure is maintained without collapse
even after repeated intense expansion and contraction by the active
substance particles, and consequently it is possible for the
charge/discharge cycle in lithium ion secondary batteries to be increased
dramatically.

[0004] The problem to be solved in the present invention is to provide a
polyimide precursor and a polyimide precursor solution that can bind the
active substance particles and the current collector body more strongly,
and a mixture slurry that can further increase the charge/discharge cycle
in lithium ion secondary batteries and the like.

Means to Solve the Problem

[0005] A polyimide precursor solution relating to a first aspect of the
present invention contains a tetracarboxylic acid ester compound, a
diamino compound having anionic groups, and a solvent. The
tetracarboxylic acid ester compound and the diamino compound are
dissolved in this solvent.

[0007] The tetracarboxylic acid ester compound can be obtained extremely
simply via esterification of the corresponding tetracarboxylic acid
dianhydride in alcohol. Furthermore, the esterification of the
tetracarboxylic acid dianhydride is preferably carried out at a
temperature of 50° C. or above and 150° C. or below.

[0010] Furthermore, tetracarboxylic acid ester compounds can be
constructed by other methods, for example, by direct esterification of
tetracarboxylic acids.

[0011] Furthermore, among the tetracarboxylic acid ester compounds for the
polyimide precursor solution relating to a first aspect of the present
invention, 3,3',4,4'-benzophenonetetracarboxylic acid diester is
particularly preferred.

[0013] Furthermore, within the range that does not compromise the scope of
the present invention, the polyimide precursor solution relating to the
present aspect can include diamine compounds that do not have anionic
groups.

[0015] Moreover, the molar ratio for the tetracarboxylic acid ester
compound and the diamine compound is usually within the range of 55:45 to
45:55. Furthermore, the abovementioned molar ratio for the
tetracarboxylic acid ester compound and the diamine compound can be
suitably changed to a ratio different from that described above provided
that the scope of the present invention is not compromised.

[0016] The solvent dissolves the tetracarboxylic acid ester compound and
the diamino compound. Examples of the solvent include preferably the type
of alcohol used to form the abovementioned tetracarboxylic acid ester.
Furthermore, in addition to the type of alcohol, N-methyl-2-pyrrolidone,
dimethylacetamide, aromatic hydrocarbons, and the like can be added to
this solvent.

[0017] Furthermore, conductive fillers, dispersing agents, and the like
can be included in the polyimide precursor mixture.

[0018] Conductive fillers function as conductive additives. Examples of
such conductive fillers include carbon black (oil furnace black, channel
black, lamp black, thermal black, Ketjen black, acetylene black, and the
like), carbon nanotubes, carbon nanofibers, fullerenes, carbon
microcoils, graphite (natural graphite, artificial graphite, and the
like), carbon black and carbon fiber short fiber (PAN carbon short fiber,
pitch carbon fiber short fiber, and the like), and the like. Such
conductive fillers can be used singly or in combinations. Additionally, a
dispersing agent is added to make a uniform dispersion of the active
substance particles in the mixture slurry. Furthermore, examples of such
dispersing agents include sorbitan monooleate, N,N-dimethyllaurylamine,
N,N-dimethylstearylamine, N-(coco alkyl)-1,3-diaminopropane, and the
like. Furthermore, such dispersing agents can be used singly or in
combinations.

[0019] In addition, for the conductive fillers to be uniformly dispersed
in the polyimide precursor solutions that contain such conductive
fillers, it is preferable for them to be adequately kneaded in a kneading
machine such as a roller mill, attritor, ball mill, pebble mill, sand
mill, Kady mill, Mechano-Fusion, stone mill, or the like.

[0020] In the mixture slurry relating to a second aspect of the present
invention, the polyimide precursor solution relating to the first aspect
furthermore contains active substance particles.

[0022] Examples of silicon alloys include solid solutions of silicon with
one or more other elements, intermetallic compounds of silicon with one
or more other elements, eutectic alloys of silicon with one or more other
elements, and the like. Examples of methods for preparing silicon alloys
include the arc fusion method, liquid quenching method, mechanical
alloying method, sputtering method, chemical vapor deposition method,
calcining method, and the like. In particular, examples of the liquid
quenching method include the single roller method, the double roller
method, and various kinds of atomizer methods such as the gas atomizer
method, water atomizer method, disk atomizer method, and the like.

[0023] Moreover, the active substance particles can be core-shell type
active substance particles in which the aforementioned active substance
particles are coated with a metal or the like. Such core-shell type
active substance particles can be manufactured using an electroless
deposition method, electrolytic method, chemical reduction method,
evaporation method, sputtering method, chemical vapor deposition method,
or the like. The shell part is preferably formed from the same metal used
to form the current collector body. The calcining of such active
substance particles greatly increases their bonding ability toward the
current collector body, and can provide superior charge/discharge cycle
characteristics. Additionally, the active substance particles can also
include materials to be alloyed with lithium. Examples of such materials
include germanium, tin, lead, zinc, magnesium, sodium, aluminum, gallium,
indium, alloys thereof, and the like.

[0024] In addition, the active substance particles can undergo surface
treatment with a silane coupling agent. If active substance particles are
treated in this manner, along with the active substance particles being
well dispersed in the mixture slurry, the active substance binding
ability toward polyimide resin can be increased.

[0025] The active substance particles preferably have an average particle
diameter of 0.5 μm or greater and less than 20 μm, and more
preferably 0.5 μm or greater and less than 10 μm. The smaller the
particle diameter of the active substance particles, the better the cycle
characteristics obtained will tend to be. Furthermore, said average
particle diameter is measured by a laser diffraction/scattering method
using a Microtrac MT3100II, particle diameter distribution measuring
apparatus (Nikkiso Co., Ltd.). Additionally, the absolute value of the
expansion/contraction of the active substance particle volume associated
with the absorption/desorption of lithium in the charging-discharging
reaction becomes smaller when active substance particles with a smaller
average particle diameter are used. For this reason, the absolute amount
of distortion between the active substance particles within the
electrodes during the charging-discharging reaction also becomes smaller.
Consequently, no destruction of the polyimide resin template occurs,
deterioration of the current collection properties of the electrode is
suppressed, and it is possible to obtain good charging and discharging
characteristics. Moreover, it is preferable for the particle size
distribution of the active substance particles to be as narrow as
possible. If the particle size distribution is broad, there will be
significant differences in size between the active substance particles,
and since significant absolute differences will be present in the
expansion/contraction in the volume associated with the
absorption/desorption of lithium, distortions will occur within the
active substance layers, and there is increased concern that destruction
of the polyimide resin template will occur.

[0026] Furthermore, the active substance particles are present in a
dispersed state in the polyimide precursor varnish comprising primarily a
tetracarboxylic acid ester compound, a diamino compound with anionic
groups, and a solvent. Additionally, the active substance particles
relating to this aspect are the active substance particles used for
anodes in the nonaqueous secondary batteries among lithium ion secondary
batteries.

[0027] A polyimide precursor relating to a third aspect of the present
invention contains a tetracarboxylic acid ester compound, and a diamino
compound having anionic groups.

[0028] The "tetracarboxylic acid ester compound" and "diamino compound
having anionic groups" are the same "tetracarboxylic acid ester compound"
and "diamino compound having anionic groups" as described in the first
aspect. In addition, the polyimide precursor can also contain the
abovementioned conductive fillers and dispersing agents. Such polyimide
precursors can be obtained by mixing together the "tetracarboxylic acid
ester compound" and "diamino compound having anionic groups", and can
also be obtained by drying the abovementioned polyimide precursor
solution. Furthermore, the "tetracarboxylic acid ester compound" and
"diamino compound having anionic groups" can be in solution form or in
powder form.

[0029] A polyimide resin relating to a fourth aspect of the present
invention can be obtained by heating the polyimide precursor solution
relating to the first aspect, or by heating the polyimide precursor
relating to the third aspect.

[0030] A polyimide resin relating to a fifth aspect of the present
invention that is the polyimide resin relating to the fourth aspect with
a glass transition temperature of 300° C. or higher.

[0031] A polyimide resin relating to a sixth aspect of the present
invention that is the polyimide resin relating to either the fourth or
fifth aspect having a molecular weight between crosslinks of 30 or less.
Furthermore, the molecular weight between crosslinks is preferably 20 or
less, and further preferably 10 or less. Furthermore, when the molecular
weight between crosslinks is smaller, three-dimensional crosslinks will
appear. The molecular weight between crosslinks is an important factor
for studying the point binding of the adherend.

[0032] A polyimide resin relating to a seventh aspect of the present
invention is the polyimide resin relating to any one of the fourth
through sixth aspects having amide groups.

[0033] An electrode relating to an eighth aspect of the present invention
is equipped with a current collector body and an active substrate layer.

[0034] The current collector body is preferably a conductive metal foil.
Such a conductive metal foil can be formed from a metal such as copper,
nickel, iron, titanium, cobalt, or the like, or can be formed from an
alloy obtained from combinations of such metals.

[0035] In addition, it is preferable to conduct surface roughening to
increase the binding between the current collector body and the active
substance layer. Furthermore, surface roughening of the current collector
body can also be carried out by providing electrolytic copper or an
electrolytic copper alloy on the surface of the foil. Additionally,
surface roughening of the current collector body can also be carried out
by using a surface roughening treatment. Examples of such surface
roughening treatments include vapor phase epitaxy, etching, grinding, and
the like. Examples of vapor phase epitaxy methods include the sputtering
method, CVD method, chemical vapor deposition method, and the like.
Examples of etching methods include the physical etching method, chemical
etching method, and the like. Examples of grinding methods include
grinding with sandpaper, grinding by the blast method, and the like.

[0036] Moreover, to increase the binding of the active substance layer, an
undercoat layer can be formed on the current collector body. The
undercoat layer is preferably formed from a resin that can adhere well to
the polyimide resin and a conductive filler that imparts conductivity to
the undercoat. For example, the undercoat layer is preferably formed by a
chemical dispersing a conductive filler into the abovementioned monomeric
polyimide precursor solution, or a chemical dispersing a conductive
filler into a polyamic acid polyimide precursor solution.

[0038] When an undercoat layer is formed on the current collector body as
described above, it is preferable to apply the abovementioned mixture
slurry after the "polyimide resin solution with conductive filler" used
to form the undercoat layer undergoes heating at a sufficient temperature
between 50° C., and 100° C. for several tens of minutes. If
done in this manner, the abovementioned mixture slurry will be applied
when the undercoat layer is not yet completely in a solidified state,
which will give good adhesion between the undercoat layer and the active
substance layer.

[0039] Furthermore, the current collector body relating to this aspect is
a current collector body used for anodes in non-aqueous secondary
batteries such as lithium ion secondary batteries, and so on.

[0040] The active substance layer is obtained from the abovementioned
mixture slurry. In addition, this active substance layer is coated onto
the current collector body. In other words, the active substance layer is
formed on the current collector body. Furthermore, this active substance
layer is primarily composed of active substance particles and polyimide
resin. The polyimide resin in this active substance layer has a porous
structure, which functions as a template material to enclose the active
substances, and along with binding the active substance particles within
these pores, it plays a role in the binding between the active substance
particles and the current collector body. Furthermore, at this time, the
polyimide resin will generally have a porosity in the range of from 20
parts by volume to 40 parts by volume. Additionally, as mentioned above,
this polyimide resin will have anionic groups. Furthermore, the polyimide
resin will primarily be formed from units derived from a tetracarboxylic
acid and units derived from a diamine. Thus, as mentioned above, the
anionic groups are bonded to the diamine-derived units.

[0041] In forming the electrode relating to the present aspect from the
abovementioned mixture slurry, after the abovementioned mixture slurry is
coated onto the current collector body or onto the undercoat layer, this
coating can be calcined. Furthermore, it is preferable for the calcining
of the coating to be conducted under a non-oxidizing atmosphere such as a
vacuum, a nitrogen atmosphere, an argon atmosphere, or the like, or under
a reducing atmosphere such as a hydrogen atmosphere, or the like. The
calcining temperature is preferably at or above the temperature at which
the monomeric polyimide precursor in the above-described mixture slurry
will become a suitably high-molecular-weight polymer through imidization,
and at or below the melting point of current collector body and the
active substance particles. Furthermore, the recommended calcining
temperature for the mixture slurry relating to the present aspect is
between 100° C. and 400° C. Furthermore, the calcining
temperature for this mixture slurry is more preferably between
100° C. and 300° C., still further preferably between
150° C. and 300° C., and still further preferably between
200° C. and 300° C. Along with avoiding deterioration of
the current collector body due to heat, this serves to preserve the
crosslinked structure of the polyimide resin. Examples of calcining
methods include the use of a common constant temperature oven, plasma
discharge sintering, the hot press method, and the like. By using such
methods to form the active substance layer on the current collector body
or the undercoat layer, the porous polyimide layer provides strong
binding not only mutually between the active substance particles in the
active substance layer, but also between the active substance particles
and the current collector body.

[0042] Additionally, before calcining the coating, this coating can be
rolled together with the current collector body, or the rolling can be
omitted, but it is preferable to omit the rolling. Furthermore, if the
"packing density of the active substance particles in the coating", the
"adhesiveness between active substance particles", or the "adhesiveness
between active substance particles and the current collector body"
becomes excessively high when the coating and the current collector body
are rolled, this will decrease the lifetime of the charging/discharging
cycle. On the other hand, if the rolling is not done, this avoids
damaging the current collector body or the polyimide resin template, with
the result that good charging/discharging cycle properties will be
obtained.

[0043] In the electrode relating to the present aspect, the polyimide
resin content in the active substance layer is preferably 5 wt % or more
and 50 wt % or less based on the total weight of the active substance
layer, more preferably 5 wt % or more and 30 wt % or less, and further
preferably 5 wt % or more and 20 wt % or less. Moreover, the volume
content of the polyimide resin in the active substance layer is
preferably 5 vol % or more and 50 vol % or less based on the total volume
of the active substance layer. If the polyimide content in the active
substance layer is less than 5 wt % or 5 vol %, there will be
insufficient mutual adhesion between the active substance particles or
insufficient adhesion between the active substance particles and the
current collector body, and if the polyimide content in the active
substance layer exceeds 50 wt % or 50 vol %, the resistance within the
electrode will increase and the initial charging might be difficult.

[0044] The method for producing a mixture slurry relating to a ninth
aspect of the present invention has a first mixing step and a second
mixing step. In the first mixing step, a polyimide precursor solution
with carbon black is prepared by mixing carbon black into monomeric
polyimide precursor solution so as not to apply the shear stress
substantially. Furthermore, the expression "so as not to apply the shear
stress substantially" means that a degree of shear stress is permissible
only if no damage to the carbon black fibers occurs.

[0045] Moreover, the monomeric polyimide precursor solution contains a
tetracarboxylic acid ester compound, a diamine compound having anionic
groups, and a solvent. Furthermore, the tetracarboxylic acid ester
compound and the diamino compound are dissolved in the solvent. In the
second mixing step, a mixture slurry is prepared by mixing active
substance particles into the polyimide precursor solution with carbon
black. Furthermore, based on 100 parts by weight of the active substance
particles, the solids fraction of the monomeric polyimide precursor
solution is preferably within the range from 5 parts by weight to 11
parts by weight.

[0046] Thus, if this method for preparing the mixture slurry is utilized,
the carbon black will not be damaged and the carbon black will be
dispersed in the monomeric polyimide precursor solution. Consequently, if
this method for preparing the mixture slurry is utilized, the active
substance layer obtained from this method for preparing the mixture
slurry will have good conductivity.

[0047] The method for producing an electrode relating to a tenth aspect of
the present invention has a coating step and the heating step. In the
coating step, the abovementioned mixture slurry is coated onto a current
collector body to form a mixture slurry coating on the current collector
body. Furthermore, an undercoat layer can already have been formed on the
current collector body. In the heating step, the mixture slurry coating
is heated to form a porous active substance layer. Furthermore, in the
heating step, the mixture slurry coating is preferably heated to a
temperature of 100° C. or above and less than 400° C., and
is further preferably heated to a temperature of 150° C. or above
and less than 350° C.

[0048] In addition, to improve the "active substance packing density",
"adhesiveness between the active substance particles", and "adhesiveness
between the active substance particles and the collector body", the
active substance layer and current collector body are usually rolled when
the electrode is formed. However, a porous active substance layer is
formed from the mixture slurry in this electrode formation method. In
other words, the active substance layer is not rolled in this electrode
formation method. In this way, the polyimide resin in the active
substance layer is made porous, and the active substance particles are
enclosed in the polyimide resin that has been made porous. For this
reason, the active substance particles are unlikely to fall out of the
polyimide resin even with repeated intense expansion and contraction by
the active substance particles.

[0049] Additionally, the mixture slurry coating is heated at a relatively
low temperature in this electrode formation method. For this reason, the
polyimide resin can be relatively flexible if this electrode formation
method is utilized. Consequently, it will be easier for the polyimide
resin to accommodate the expansion of the active substance particles if
this electrode formation method is utilized, and the active substance
particles can be prevented from falling out of the polyimide resin.

EFFECT OF THE INVENTION

[0050] The polyimide precursor solution and the polyimide precursor
relating to the present invention can provide stronger binding (in
particular, point binding) between the active substance particles and the
current collector body compared to conventional polyimide precursor
solutions and polyimide precursor. And when the polyimide precursor
solutions and polyimide precursor are utilized as a binder for the anode
active substance layer in a lithium ion secondary battery, further
improved charging/discharging cycle times are expected for lithium ion
secondary batteries and the like.

[0051] Moreover, when the polyimide precursor solution and the polyimide
precursor relating to the present invention are utilized as a binder for
the active substance particles, not only can stronger binding (in
particular, point binding) between the active substance particles and the
current collector body be expected, but also promotion of the uptake of
cations (lithium ions and the like) by the free carboxyl groups, which
can improve the discharge capacity of lithium ion secondary batteries and
the like.

BRIEF EXPLANATION OF DIAGRAMS

[0052]FIG. 1 is a chart of measurements using Fourier transform infrared
(FT-IR) spectroscopy on strips of polyimide film relating to Working
Example 1 of the present invention and Comparative Example 1.

[0053]FIG. 2 is a chart of dynamic viscoelasticity measurements of strips
of polyimide film relating to Working Example 1 of the present invention
and Comparative Example 1.

MODES FOR IMPLEMENTING THE INVENTION

[0054] The present invention is explained in further detail below using
working examples. Furthermore, the working examples shown below are for
illustration only, and do not limit the present invention in any way.

Working Example 1

[0055] 1. Preparation of the Monomeric Polyimide Precursor Solution

[0056] The synthesis vessel was a 500 mL 3-neck flask equipped with a
stirring shaft that was fitted with a polytetrafluoroethylene stir
paddle. Then, after this synthesis vessel was charged with 10.19 g (0.032
mol) 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride (Daicel
Chemical Industries, BTDA), and 2.91 g (0.063 mol) ethanol (Ueno Chemical
Industries, Ltd.), the synthesis vessel contents were heated to
90° C. with stirring for 1 hr to prepare a BTDA diester solution
as a polyimide precursor solution with a solids fraction of 28 wt %.
After the BTDA diester solution was cooled to 45° C. or below,
4.81 g (0.032 mol) of 3,5-diaminobenzoic acid (Tokyo Kasei Industries,
Ltd., 3,5-DABA) was added and this was heated again to 50° C. with
stirring for 1 hr to prepare the monomeric polyimide precursor solution.

[0057] 2. Preparation of a Lithium Ion Secondary Battery

[0058] (1) Preparation of the Anode The abovementioned monomeric polyimide
precursor solution was filtered through a #300 SUS mesh. After this
filtration, a film was prepared from the monomeric polyimide precursor
solution, and measurement of the glass transition temperature (Tg)
showed it to be 331° C. A film prepared from the polyimide
precursor solution after filtration gave a lower Tg than a film
prepared from the polyimide precursor solution before filtration, but
this was believed due to removal of impurities by the filtration or to
experimental error. To 7.3 g of this monomeric polyimide precursor
solution after filtration was added 39.0 g of silicon powder (Fukuda
Metal Foil & Powder Co., Ltd., purity 99.9%, average particle diameter
2.1 μm), and 2.4 g Ketjen black (Fukuda Metal Foil & Powder Co., Ltd.,
primary particle diameter 39.5 nm), followed by thorough mixing using a
planetary (self-revolving) type mixer (Shinkey) to prepare the anode
mixture slurry.

[0059] After coating this anode mixture slurry onto one side (rough
surface) of an electrolytic copper foil (thickness: 35 μm) as the
current collector body to give a surface roughness (arithmetic mean
roughness) Rz of 4.0 μm, the thickness of the prepared dried anode
intermediate after drying was 19 μm. The anode intermediate was cut
into circular shapes with a diameter of 11 mm, and underwent heat
treatment at 300° C. for 1 hr (calcining) under a nitrogen
atmosphere to prepare a calcined anode.

[0060] (2) Counter Electrode

[0061] The counter electrode was prepared by cutting lithium metal foil
(thickness: 0.5 mm) into circular shapes with a diameter of 13 mm.

[0062] (3) Nonaqueous Electrolyte

[0063] A mixture of ethylene carbonate and diethyl carbonate in a ratio of
1:1 (v/v) was prepared, and LiPF6 was dissolved therein to give 1
mole/L, and this was used as the nonaqueous electrolyte.

[0066] Furthermore, the cathode and counter electrode were arranged to
face each other via a polypropylene separator (Celgard 2400, Celgard Co.)
reinforced with glass fiber fabric.

[0067] 3. Measurement of Various Properties

[0068] (1) Confirmation of the Amide Group by Fourier Transform Infrared
(FT-IR) Spectroscopy

[0069] After casting the abovementioned monomeric polyimide precursor
solution onto a glass plate, this was stretched thin using a doctor blade
and was calcined at 200° C. for 1 hr, 250° C. for 1 hr,
300° C. for 1 hr, and 350° C. for 1 hr. Then, the piece of
polyimide film formed on the glass plate was peeled off from the glass
plate to obtain the piece of polyimide film.

[0070] Next, this piece of polyimide film was placed in an FTIR-8400
instrument (Shimadzu Corp.), and the FT-IR measurement was carried out
using the thin-film transmission method. In the IR spectrum obtained,
confirmation came from the peaks in the vicinity of 3350 cm-1 and
3100 cm-1 belonging to the unassociated and associated amide group
N-H stretching modes, respectively. (see FIG. 1). Consequently, the
presence of amide groups in this piece of polyimide film was confirmed.
Therefore, it was presumed that the carboxyl groups of the diaminobenzoic
acid were converted to amide groups by heating.

[0071] (2) Measurement of the Glass Transition Temperature (Tg)

[0072] After casting the abovementioned monomeric polyimide precursor
solution onto a glass plate, this was stretched thin using a doctor blade
and was calcined at 200° C. for 1 hr, 250° C. for 1 hr,
300° C. for 1 hr, and 350° C. for 1 hr. Then, the piece of
polyimide film formed on the glass plate was peeled off from the glass
plate to obtain the piece of polyimide film.

[0073] After this piece of polyimide film was placed in an EXSTAR 6000,
dynamic viscoelasticity measuring instrument (Seiko Instruments), the
storage elastic modulus was measured at a frequency of 1 Hz and a
temperature program of 2° C./min to obtain the storage elastic
modulus curve for this piece of polyimide film. As shown in FIG. 2, the
glass transition temperature (Tg) for this piece of polyimide film
was the temperature that corresponds to the intersection point between
"an extrapolation from the low-temperature, straight-line portion of the
storage modulus curve", and "the tangential line at the point considered
to have the maximum slope in the glass transition region of the curve".
The glass transition temperature (Tg) for this piece of polyimide
film was 339° C.

[0074] (3) Molecular Weight Between Crosslinks (Mx)

[0075] After casting the abovementioned monomeric polyimide precursor
solution onto a glass plate, this was stretched thin using a doctor blade
and was calcined at 200° C. for 1 hr, 250° C. for 1 hr,
300° C. for 1 hr, and 350° C. for 1 hr to prepare a piece
of polyimide film.

[0076] After this piece of polyimide film was placed in an EXSTAR 6000,
dynamic viscoelasticity measuring instrument (Seiko Instruments), the
storage elastic modulus was measured at a frequency of 1 Hz and a
temperature program of 2° C./min to obtain the storage elastic
modulus curve for this piece of polyimide film. The molecular weight
between crosslinks (Mx) for this piece of polyimide film was
determined by the following formula (1): Furthermore, in formula (1),
ρ is the density of the polyimide (1.3 g/cm3), T is the absolute
temperature at the point where the storage elastic modulus is extremely
small, E' is the storage elastic modulus at the extremely small point,
and R is the gas constant. The molecular weight between crosslinks
(Mx) for this piece of polyimide film was 2.9 (see FIG. 2)

Mx=ρRT/E' (1)

[0077] (4) Cross-Cut Adhesion Test

[0078] After grinding a CF-T8 copper foil (Fukuda Metal Foil & Powder Co.,
Ltd., thickness: 18 μm) using P-2000C-Cw sandpaper (Japan Sandpaper),
the sanded surface of this copper foil was coated with the abovementioned
monomeric polyimide precursor solution to have a film thickness value of
between approximately 10 μm and 20 μm after calcining. Thus, after
this monomeric polyimide precursor solution was dried under an air
atmosphere for 10 min at 100° C., it was heated to 220° C.
under reduced pressure for 1 hr, then calcined at 250° C. under an
air atmosphere for 1 hr, and then at 275° C. for 1 hr to give the
test piece.

[0079] The adhesion strength of the polyimide resin toward copper foil was
measured according to the "General Rules of Coating Films for Automobile
Parts 4.15, cross-cut adhesion test method (JIS D0202 (1998))".
Furthermore, "Askul cellophane tape" from the Askul Co. was used for the
cellophane tape. The result was that the adhesion strength of the
polyimide resin toward copper foil was 28/100.

[0080] In addition, after grinding a silicon wafer (Fujimi Fine Technology
Inc., "4 in. silicon wafer, mirror surface finish, semiconductor
handling") using P-2000C-Cw sandpaper (Japan Sandpaper), this sanded
surface of this silicon wafer was coated with the abovementioned
monomeric polyimide precursor solution to have a film thickness value of
between approximately 10 μm and 30 μm after calcining Thus, after
this monomeric polyimide precursor solution was dried under an air
atmosphere for 10 min at 100° C., it was heated to 220° C.
under reduced pressure for 1 hr, then calcined at 250° C. under an
air atmosphere for 1 hr, and then at 275° C. for 1 hr to give the
test piece.

[0081] The adhesion strength of the polyimide resin toward silicon wafer
was measured according to the "General Rules of Coating Films for
Automobile Parts 4.15, cross-cut adhesion test method (JIS D0202
(1998))". Furthermore, "Askul cellophane tape" from the Askul Co. was
used for the cellophane tape. The result was that the adhesion strength
of the polyimide resin toward the silicon wafer was 100/100.

[0083] A charging/discharging cycle test was carried out on the lithium
ion secondary battery. The charging/discharging cycle test was carried
out for 50 charging/discharging cycles at an ambient temperature of
30° C., charging/discharging rate of 0.1 C, a voltage cut-off of
0.0 V while charging and 1.0 V while discharging, and the discharge
capacity in mAh/g was measured every cycle. Additionally, the maintenance
factor was determined as the "ratio of the discharge capacity for the
30th cycle to the discharge capacity for the 2nd cycle" and
"ratio of the discharge capacity for the 50th cycle to the discharge
capacity for the 2nd cycle". Furthermore, the specific capacity of
the electrode surface of this lithium ion secondary battery was 4.62
mAh/cm2 (see Table 1).

[0084] The results were that the discharge capacity was 4309.6 mAh/g for
the 1st cycle, 3584.8 mAh/g for the 2nd cycle, 3115.0 mAh/g for
the 30th cycle, and 2689.8 mAh/g for the 50th cycle. In
addition, the ratio of discharge capacities (maintenance factors) for the
30th cycle vs. the 2nd cycle was
(3115.0/3584.8)×100=86.89%, and for 50th cycle vs. the
2nd cycle was (2689.8/3584.8)×100=75.03% (see Table 1).

Working Example 2

[0085] Except for "preparing the dried anode intermediate after applying a
coating of the anode mixture slurry to one surface of an electrolytic
copper foil to give a thickness of 14 μm after drying", a battery was
prepared in the same manner as for Working Example 1, and its
charging/discharging cycle characteristics were measured in the same
manner as for Working Example 1. Furthermore, the specific capacity of
the electrode surface of this lithium ion secondary battery was 4.70
mAh/cm2 (see Table 2).

[0086] The results were that the discharge capacity was 4194.7 mAh/g for
the 1st cycle, 3470.1 mAh/g for the 2nd cycle, 3026.7 mAh/g for
the 30th cycle, and 2614.1 mAh/g for the 50th cycle. In
addition, the ratio of discharge capacities (maintenance factors) for the
30th cycle vs. the 2nd cycle was
(3026.7/3470.1)×100=87.22%, and for 50th cycle vs. the
2nd cycle was (2614.1/3470.1)×100=75.33% (see Table 2).

Working Example 3

[0087] Except for "preparing the dried anode intermediate after applying a
coating of the anode mixture slurry to one surface of an electrolytic
copper foil to give a thickness of 23 μm after drying" and "preparing
the calcined anode by cutting the anode intermediate into circular pieces
11 mm in diameter which were then subjected to heat treatment (calcining)
at 350° C. for 4 hr under a nitrogen atmosphere", a battery was
prepared in the same manner as for Working Example 1, and its
charging/discharging cycle characteristics were measured in the same
manner as for Working Example 1. Furthermore, the specific capacity of
the electrode surface of this lithium ion secondary battery was 4.75
mAh/cm2 (see Table 2).

[0088] The results were that the discharge capacity was 4238.8 mAh/g for
the 1st cycle, 3500.8 mAh/g for the 2nd cycle, 3014.6 mAh/g for
the 30th cycle, and 2601.3 mAh/g for the 50th cycle. In
addition, the ratio of discharge capacities (maintenance factors) for the
30th cycle vs. the 2nd cycle was
(3014.6/3500.8)×100=86.11%, and for 50th cycle vs. the
2nd cycle was (2601.3/3500.8)×100=74.31% (see Table 2).

Working Example 4

[0089] Except for "preparing the dried anode intermediate after applying a
coating of the anode mixture slurry to one surface of an electrolytic
copper foil to give a thickness of 16 μm after drying" and "preparing
the calcined anode by cutting the anode intermediate into circular pieces
11 mm in diameter which were then subjected to heat treatment (calcining)
at 350° C. for 4 hr under a nitrogen atmosphere", a battery was
prepared in the same manner as for Working Example 1, and its
charging/discharging cycle characteristics were measured in the same
manner as for Working Example 1. Furthermore, the specific capacity of
the electrode surface of this lithium ion secondary battery was 4.80
mAh/cm2 (see Table 2).

[0090] The results were that the discharge capacity was 4121.4 mAh/g for
the 1st cycle, 3414.3 mAh/g for the 2nd cycle, 2945.5 mAh/g for
the 30th cycle, and 2544.7 mAh/g for the 50th cycle. In
addition, the ratio of discharge capacities (maintenance factors) for the
30th cycle vs. the 2nd cycle was
(2945.5/3414.3)×100=86.27%, and for 50th cycle vs. the
2nd cycle was (2544.7/3414.3)×100=74.53% (see Table 2).

Working Example 5

[0091] Except for "preparing the dried anode intermediate after applying a
coating of the anode mixture slurry to one surface of an electrolytic
copper foil to give a thickness of 15 μm after drying" and "preparing
the calcined anode by cutting the anode intermediate into circular pieces
11 mm in diameter which were then subjected to heat treatment (calcining)
at 350° C. for 4 hr under a nitrogen atmosphere", a battery was
prepared in the same manner as for Working Example 1, and its
charging/discharging cycle characteristics were measured in the same
manner as for Working Example 1. Furthermore, the specific capacity of
the electrode surface of this lithium ion secondary battery was 4.90
mAh/cm2 (see Table 2).

[0092] The results were that the respective discharge capacity was 4144.9
mAh/g for the 1st cycle, 3412.6 mAh/g for the 2nd cycle, 2959.5
mAh/g for the 30th cycle, and 2531.3 mAh/g for the 50th cycle.
In addition, the ratio of discharge capacities (maintenance factors) for
the 30th cycle vs. the 2nd cycle was
(2959.5/3412.6)×100=86.72%, and for 50th cycle vs. the
2nd cycle was (2531.3/3412.6)×100=74.18% (see Table 2).

Working Example 6

[0093] Except for "using 43.3780 g silicon powder (Fukuda Metal Foil &
Powder Co., Ltd.; purity: 99.9%; average particle diameter: 0.9 μm) in
the preparation of the anode", "preparing the dried anode intermediate
after applying a coating of the anode mixture slurry to one surface of an
electrolytic copper foil to give a thickness of 1 μm after drying" and
"preparing the calcined anode by cutting the anode intermediate into
circular pieces 11 mm in diameter which were then subjected to heat
treatment (calcining) at 200° C. for 10 hr under a nitrogen
atmosphere", a battery was prepared in the same manner as for Working
Example 1, and its charging/discharging cycle characteristics were
measured in the same manner as for Working Example 1. Furthermore, the
specific capacity of the electrode surface of this lithium ion secondary
battery was 1.82 mAh/cm2 (see Table 2).

[0094] The results were that the discharge capacity was 4425.8 mAh/g for
the 1st cycle, 3843.5 mAh/g for the 2nd cycle, 3364.5 mAh/g for
the 30th cycle, and 3021.8 mAh/g for the 50th cycle. In
addition, the ratio of discharge capacities (maintenance factors) for the
30th cycle vs. the 2nd cycle was
(3364.5/3843.5)×100=87.54%, and for 50th cycle vs. the
2nd cycle was (3021.8/3843.5)×100=78.62% (see Table 2).

Working Example 7

[0095] Except for "using 43.0836 g silicon powder (Fukuda Metal Foil &
Powder Co., Ltd.; purity: 99.9%; average particle diameter: 0.9 μm) in
the preparation of the anode", "preparing the dried anode intermediate
after applying a coating of the anode mixture slurry to one surface of an
electrolytic copper foil to give a thickness of 3 μm after drying" and
"preparing the calcined anode by cutting the anode intermediate into
circular pieces 11 mm in diameter which were then subjected to heat
treatment (calcining) at 200° C. for 10 hr under a nitrogen
atmosphere", a battery was prepared in the same manner as for Working
Example 1, and its charging/discharging cycle characteristics were
measured in the same manner as for Working Example 1. Furthermore, the
maintenance factor was determined in this working example as the "ratio
of the discharge capacity after 10 cycles to the discharge capacity after
2 cycles". Furthermore, the specific capacity of the electrode surface of
this lithium ion secondary battery was 2.12 mAh/cm2 (see Table 3).

[0096] The results were that the discharge capacity was 3541.5 mAh/g for
the 1st cycle, 3076.5 mAh/g for the 2nd cycle, 3026.4 mAh/g for
the 10th cycle, 2803.4 mAh/g for the 30th cycle, and 2424.6
mAh/g for the 50th cycle. In addition, the ratio of discharge
capacities (maintenance factors) for the 10th cycle vs. the 2nd
cycle was (3026.4/3076.5)×100=98.37%, for the 30th cycle vs.
the 2nd cycle was (2803.4/3076.5)×100=91.12%, and for
50th cycle vs. the 2nd cycle was
(2424.6/3076.5)×100=78.81% (see Table 3).

Working Example 8

[0097] Except for "using 43.3780 g silicon powder (Fukuda Metal Foil &
Powder Co., Ltd.; purity: 99.9%; average particle diameter: 0.9 μm) in
the preparation of the anode", and "preparing the dried anode
intermediate after applying a coating of the anode mixture slurry to one
surface of an electrolytic copper foil to give a thickness of 1 μm
after drying", a battery was prepared in the same manner as for Working
Example 1, and its charging/discharging cycle characteristics were
measured in the same manner as for Working Example 1. Furthermore, the
specific capacity of the electrode surface of this lithium ion secondary
battery was 1.69 mAh/cm2 (see Table 3).

[0098] The results were that the discharge capacity was 4700.7 mAh/g for
the 1st cycle, 4124.8 mAh/g for the 2nd cycle, 3401.5 mAh/g for
the 30th cycle, and 2955.6 mAh/g for the 50th cycle. In
addition, the ratio of discharge capacities (maintenance factors) for the
30th cycle vs. the 2nd cycle was
(3401.5/4124.8)×100=82.46%, and for 50th cycle vs. the
2nd cycle was (2955.6/4124.8)×100=71.65% (see Table 3).

Working Example 9

[0099] Except for "using 43.0836 g silicon powder (Fukuda Metal Foil &
Powder Co., Ltd.; purity: 99.9%; average particle diameter: 0.9 μm) in
the preparation of the anode", and "preparing the dried anode
intermediate after applying a coating of the anode mixture slurry to one
surface of an electrolytic copper foil to give a thickness of 1 μm
after drying", a battery was prepared in the same manner as for Working
Example 1, and its charging/discharging cycle characteristics were
measured in the same manner as for Working Example 1. Furthermore, the
specific capacity of the electrode surface of this lithium ion secondary
battery was 2.00 mAh/cm2 (see Table 3).

[0100] The results were that the discharge capacity was 3898.5 mAh/g for
the 1st cycle, 3384.8 mAh/g for the 2nd cycle, 2997.9 mAh/g for
the 30th cycle, and 2559.5 mAh/g for the 50th cycle. In
addition, the ratio of discharge capacities (maintenance factors) for the
30th cycle vs. the 2nd cycle was
(2997.9/3384.8)×100=88.57%, and for 50th cycle vs. the
2nd cycle was (2559.5/3384.8)×100=75.62% (see Table 3).

Working Example 10

[0101] Except for "using 43.3780 g silicon powder (Fukuda Metal Foil &
Powder Co., Ltd.; purity: 99.9%; average particle diameter: 0.9 μm) in
the preparation of the anode", "preparing the dried anode intermediate
after applying a coating of the anode mixture slurry to one surface of an
electrolytic copper foil to give a thickness of 1 μm after drying" and
"preparing the calcined anode by cutting the anode intermediate into
circular pieces 11 mm in diameter which were then subjected to heat
treatment (calcining) at 350° C. for 4 hr under a nitrogen
atmosphere", a battery was prepared in the same manner as for Working
Example 1, and its charging/discharging cycle characteristics were
measured in the same manner as for Working Example 1. Furthermore, the
specific capacity of the electrode surface of this lithium ion secondary
battery was 1.77 mAh/cm2 (see Table 3).

[0102] The results were that the discharge capacity was 4282.7 mAh/g for
the 1st cycle, 3748.8 mAh/g for the 2nd cycle, 3113.2 mAh/g for
the 30th cycle, and 2704.6 mAh/g for the 50th cycle. In
addition, the ratio of discharge capacities (maintenance factors) for the
30th cycle vs. the 2nd cycle was
(3113.2/3748.8)×100=83.05%, and for 50th cycle vs. the
2nd cycle was (2704.6/3748.8)×100=72.15% (see Table 3).

Working Example 11

[0103] Except for "using 43.0836 g silicon powder (Fukuda Metal Foil &
Powder Co., Ltd.; purity: 99.9%; average particle diameter: 0.9 μm) in
the preparation of the anode", "preparing the dried anode intermediate
after applying a coating of the anode mixture slurry to one surface of an
electrolytic copper foil to give a thickness of 1 μm after drying" and
"preparing the calcined anode by cutting the anode intermediate into
circular pieces 11 mm in diameter which were then subjected to heat
treatment (calcining) at 350° C. for 4 h under a nitrogen
atmosphere", a battery was prepared in the same manner as for Working
Example 1, and its charging/discharging cycle characteristics were
measured in the same manner as for Working Example 1. Furthermore, the
specific capacity of the electrode surface of this lithium ion secondary
battery was 1.95 mAh/cm2 (see Table 3).

[0104] The results were that the discharge capacity was 3714.4 mAh/g for
the 1st cycle, 3231.6 mAh/g for the 2nd cycle, 2835.7 mAh/g for
the 30th cycle, and 2405.2 mAh/g for the 50th cycle.

[0105] In addition, the ratio of discharge capacities (maintenance
factors) for the 30th cycle vs. the 2nd cycle was
(2835.7/3231.6)×100=87.75%, and for 50th cycle vs. the
2nd cycle was (2405.2/3231.6)×100=74.43% (see Table 3).

Working Example 12

[0106] Except for "using 43.3780 g silicon powder (Fukuda Metal Foil &
Powder Co., Ltd.; purity: 99.9%; average particle diameter: 0.9 μm) in
the preparation of the anode", "preparing the dried anode intermediate
after applying a coating of the anode mixture slurry to one surface of an
electrolytic copper foil to give a thickness of 1 μm after drying" and
"preparing the calcined anode by cutting the anode intermediate into
circular pieces 11 mm in diameter which were then subjected to heat
treatment (calcining) at 400° C. for 1 hr under a nitrogen
atmosphere", a battery was prepared in the same manner as for Working
Example 1, and its charging/discharging cycle characteristics were
measured in the same manner as for Working Example 1. Furthermore, the
specific capacity of the electrode surface of this lithium ion secondary
battery was 1.69 mAh/cm2 (see Table 3).

[0107] The results were that the discharge capacity was 4424.0 mAh/g for
the 1st cycle, 3873.1 mAh/g for the 2nd cycle, 3226.9 mAh/g for
the 30th cycle, and 2686.3 mAh/g for the 50th cycle. In
addition, the ratio of discharge capacities (maintenance factors) for the
30th cycle vs. the 2nd cycle was
(3226.9/3873.1)×100=83.32%, and for 50th cycle vs. the
2nd cycle was (2686.3/3873.1)×100=69.36% (see Table 3).

Working Example 13

[0108] Except for "using 43.0836 g silicon powder (Fukuda Metal Foil &
Powder Co., Ltd.; purity: 99.9%; average particle diameter: 0.9 μm) in
the preparation of the anode", "preparing the dried anode intermediate
after applying a coating of the anode mixture slurry to one surface of an
electrolytic copper foil to give a thickness of 1 μm after drying" and
"preparing the calcined anode by cutting the anode intermediate into
circular pieces 11 mm in diameter which were then subjected to heat
treatment (calcining) at 400° C. for 1 hr under a nitrogen
atmosphere", a battery was prepared in the same manner as for Working
Example 1, and its charging/discharging cycle characteristics were
measured in the same manner as for Working Example 1. Furthermore, the
specific capacity of the electrode surface of this lithium ion secondary
battery was 1.87 mAh/cm2 (see Table 4).

[0109] The results were that the discharge capacity was 3870.7 mAh/g for
the 1st cycle, 3391.8 mAh/g for the 2nd cycle, 2977.3 mAh/g for
the 30th cycle, and 2524.6 mAh/g for the 50th cycle. In
addition, the ratio of discharge capacities (maintenance factors) for the
30th cycle vs. the 2nd cycle was
(2977.3/3391.8)×100=87.78%, and for 50th cycle vs. the
2nd cycle was (2524.6/3391.8)×100=74.43% (see Table 4).

Working Example 14

[0110] Except for "using 38.9802 g silicon powder (Fukuda Metal Foil &
Powder Co., Ltd.; purity: 99.9%; average particle diameter: 0.9 μm) in
the preparation of the anode", and "preparing the dried anode
intermediate after applying a coating of the anode mixture slurry to one
surface of an electrolytic copper foil to give a thickness of 1 μm
after drying", a battery was prepared in the same manner as for Working
Example 1, and its charging/discharging cycle characteristics were
measured in the same manner as for Working Example 1. Furthermore, with
30 cycles of charging/discharging, the maintenance factors in this
working example were determined as the "ratio of the discharge capacity
for the 10th cycle to the discharge capacity for the 2nd cycle"
and "ratio of the discharge capacity for the 30th cycle to the
discharge capacity for the 2nd cycle". Furthermore, the specific
capacity of the electrode surface of this lithium ion secondary battery
was 2.07 mAh/cm2 (see Table 4).

[0111] The results were that the discharge capacity was 4448.6 mAh/g for
the 1st cycle, 3820.2 mAh/g for the 2nd cycle, 3738.1 mAh/g for
the 10th cycle, and 3448.6 mAh/g for the 30th cycle. In
addition, the ratio of discharge capacities (maintenance factors) for the
10th cycle vs. the 2nd cycle was (3738.1/3820.2)×100=97.85%,
and for 30th cycle vs. the 2nd cycle was
(3448.6/3820.2)×100=90.28% (see Table 4).

Working Example 15

[0112] Except for "using 46.9837 g silicon powder (Fukuda Metal Foil &
Powder Co., Ltd.; purity: 99.9%; average particle diameter: 0.9 μm) in
the preparation of the anode", "preparing the dried anode intermediate
after applying a coating of the anode mixture slurry to one surface of an
electrolytic copper foil to give a thickness of 4 μm after drying" and
"preparing the calcined anode by cutting the anode intermediate into
circular pieces 11 mm in diameter which were then subjected to heat
treatment (calcining) at 200° C. for 10 hr under a nitrogen
atmosphere", a battery was prepared in the same manner as for Working
Example 1, and its charging/discharging cycle characteristics were
measured in the same manner as for Working Example 1. Furthermore, with
10 cycles of charging/discharging, the maintenance factors in this
working example were determined as the "ratio of the discharge capacity
for the 10th cycle to the discharge capacity for the 2nd
cycle". Furthermore, the specific capacity of the electrode surface of
this lithium ion secondary battery was 1.67 mAh/cm2 (see Table 4).

[0113] The results were that the discharge capacity was 3736.7 mAh/g for
the 1st cycle, 3195.2 mAh/g for the 2nd cycle, and 3083.1 mAh/g
for the 10th cycle. In addition, the ratio of discharge capacities
(maintenance factor) for the 10th cycle vs. the 2nd cycle was
(3083.1/3195.2)×100=96.49% (see Table 4).

Working Example 16

[0114] Except for "using 46.9837 g silicon powder (Fukuda Metal Foil &
Powder Co., Ltd.; purity: 99.9%; average particle diameter: 0.9 μm) in
the preparation of the anode", "preparing the dried anode intermediate
after applying a coating of the anode mixture slurry to one surface of an
electrolytic copper foil to give a thickness of 4 μm after drying" and
"preparing the calcined anode by cutting the anode intermediate into
circular pieces 11 mm in diameter which were then subjected to heat
treatment (calcining) at 200° C. for 10 hr under a nitrogen
atmosphere", a battery was prepared in the same manner as for Working
Example 1, and its charging/discharging cycle characteristics were
measured in the same manner as for Working Example 1. Furthermore, with
10 cycles of charging/discharging, the maintenance factor was determined
in this working example as the "ratio of the discharge capacity after 10
cycles to the discharge capacity after 2 cycles". Furthermore, the
specific capacity of the electrode surface of this lithium ion secondary
battery was 1.49 mAh/cm2 (see Table 4).

[0115] The results were that the discharge capacity was 4022.2 mAh/g for
the 1st cycle, 3490.8 mAh/g for the 2nd cycle, and 3441.9 mAh/g
for the 10th cycle. In addition, the ratio of discharge capacities
(maintenance factor) for the 10th cycle vs. the 2nd cycle was
(3441.9/3490.8)×100=98.60% (see Table 4).

Comparative Example 1

[0116] Except for replacing 4.81 g (0.032 mol) of 3,5-diaminobenzoic acid
(3,5-DABA) with 3.47 g (0.032 mol) of meta-phenylenediamine (m-PDA), a
monomeric polyimide precursor solution was prepared in the same manner as
for Working Example 1, and its physical properties were measured in the
same manner as for Working Example 1 (see Table 1).

[0117] The results were that in the IR spectrum obtained, no peaks were
observed in the vicinity of 3350 cm-1 and 3100 cm-1. Moreover,
the polyimide resin obtained from the abovementioned monomeric polyimide
precursor solution had a glass transition temperature of 308° C.,
a molecular weight between crosslinks of 181, and an adhesion strength
toward copper foil of 0/100. Furthermore, this polyimide resin had a
weaker adhesion strength, and had already delaminated by the time it was
cut into a grid pattern with a cutter knife.

Reference Example 1

[0118] After grinding a silicon wafer (Fujimi Fine Technology Inc., "4 in.
silicon wafer, mirror surface finish, semiconductor handling") using
P-2000C-Cw sandpaper (Japan Sandpaper), the sanded surface of this
silicon wafer was coated with the abovementioned monomeric polyimide
precursor solution in the same manner as in Comparative Example 1 to have
a film thickness of between approximately 10 μm and 30 μm after
calcining. Thus, after this monomeric polyimide precursor solution was
dried under an air atmosphere for 10 min at 100° C., it was heated
to 220° C. under reduced pressure for 1 hr, then calcined at
250° C. under an air atmosphere for 1 hr, and then at 275°
C. for 1 hr to give the test piece.

[0119] The adhesion strength of the polyimide resin toward silicon wafer
was measured according to the "General Rules of Coating Films for
Automobile Parts 4.15, cross-cut adhesion test method (JIS D0202
(1998))". Furthermore, "Askul cellophane tape" from the Askul Co. was
used for the cellophane tape. The result was that the adhesion strength
of the polyimide resin toward the silicon wafer was 100/100.

[0120] Except for "replacing 4.81 g (0.032 mol) of 3,5-diaminobenzoic acid
(3,5-DABA) with 3.47 g (0.032 mol) of meta-phenylenediamine (m-PDA) in
the preparation of the monomeric polyimide precursor solution", and
"preparing the dried anode intermediate after applying a coating of the
anode mixture slurry to one surface of an electrolytic copper foil to
give a thickness of 20 μm after drying", a battery was prepared in the
same manner as for Working Example 1, and its charging/discharging cycle
characteristics were measured in the same manner as for Working Example
1. Furthermore, the specific capacity of the electrode surface of this
lithium ion secondary battery was 6.31 mAh/cm2 (see Table 5).

[0121] The results were that the discharge capacity was 3654.3 mAh/g for
the 1st cycle, 2857.9 mAh/g for the 2nd cycle, 1645.6 mAh/g for
the 30th cycle, and 1224.9 mAh/g for the 50th cycle. In
addition, the ratio of discharge capacities (maintenance factors) for the
30th cycle vs. the 2nd cycle was
(1645.6/2857.9)×100=57.58%, and for 50th cycle vs. the
2nd cycle was (1224.9/2857.9)×100=42.86% (see Table 5).
(Comparative Example 3)

[0122] Except for "replacing 4.81 g (0.032 mol) of 3,5-diaminobenzoic acid
(3,5-DABA) with 3.47 g (0.032 mol) of meta-phenylenediamine (m-PDA) in
the preparation of the monomeric polyimide precursor solution", and
"preparing the dried anode intermediate after applying a coating of the
anode mixture slurry to one surface of an electrolytic copper foil to
give a thickness of 35 μm after drying", a battery was prepared in the
same manner as for Working Example 1, and its charging/discharging cycle
characteristics were measured in the same manner as for Working Example
1. Furthermore, the specific capacity of the electrode surface of this
lithium ion secondary battery was 10.13 mAh/cm2 (see Table 5).

[0123] The results were that the discharge capacity was 3533.4 mAh/g for
the 1st cycle, 2661.4 mAh/g for the 2nd cycle, 1453.3 mAh/g for
the 30th cycle, and 1067.3 mAh/g for the 50th cycle. In
addition, the ratio of discharge capacities (maintenance factors) for the
30th cycle vs. the 2nd cycle was
(1453.3/2661.4)×100=54.61%, and for 50th cycle vs. the
2nd cycle was (1067.3/2661.4)×100=40.10% (see Table 5).

Comparative Example 4

[0124] Except for "replacing 4.81 g (0.032 mol) of 3,5-diaminobenzoic acid
(3,5-DABA) with 3.47 g (0.032 mol) of meta-phenylenediamine (m-PDA) in
the preparation of the monomeric polyimide precursor solution", and
"preparing the dried anode intermediate after applying a coating of the
anode mixture slurry to one surface of an electrolytic copper foil to
give a thickness of 27 μm after drying", a battery was prepared in the
same manner as for Working Example 1, and its charging/discharging cycle
characteristics were measured in the same manner as for Working Example
1. Furthermore, the specific capacity of the electrode surface of this
lithium ion secondary battery was 7.27 mAh/cm2 (see Table 5).

[0125] The results were that the discharge capacity was 3410.2 mAh/g for
the 1st cycle, 2757.5 mAh/g for the 2nd cycle, 1207.2 mAh/g for
the 30th cycle, and 762.8 mAh/g for the 50th cycle. In
addition, the ratio of discharge capacities (maintenance factors) for the
30th cycle vs. the 2nd cycle was
(1207.2/2757.5)×100=43.78%, and for 50th cycle vs. the
2nd cycle was (762.8/2757.5)×100=27.66% (see Table 5).

Comparative Example 5

[0126] Except for "replacing 4.81 g (0.032 mol) of 3,5-diaminobenzoic acid
(3,5-DABA) with 3.47 g (0.032 mol) of meta-phenylenediamine (m-PDA) in
the preparation of the monomeric polyimide precursor solution",
"preparing the dried anode intermediate after applying a coating of the
anode mixture slurry to one surface of an electrolytic copper foil to
give a thickness of 37 μm after drying", and "preparing the calcined
anode by cutting the anode intermediate into circular pieces 11 mm in
diameter which were then subjected to heat treatment (calcining) at
350° C. for 4 hr under a nitrogen atmosphere", a battery was
prepared in the same manner as for Working Example 1, and its
charging/discharging cycle characteristics were measured in the same
manner as for Working Example 1. Furthermore, the specific capacity of
the electrode surface of this lithium ion secondary battery was 9.50
mAh/cm2 (see Table 5).

[0127] The results were that the discharge capacity was 3780.1 mAh/g for
the 1st cycle, 2709.1 mAh/g for the 2nd cycle, 1202.9 mAh/g for
the 30th cycle, and 825.3 mAh/g for the 50th cycle. In
addition, the ratio of discharge capacities (maintenance factors) for the
30th cycle vs. the 2nd cycle was
(1202.9/2709.1)×100=44.40%, and for 50th cycle vs. the
2nd cycle was (825.3/2709.1)×100=30.46% (see Table 5).

Comparative Example 6

[0128] Except for "replacing 4.81 g (0.032 mol) of 3,5-diaminobenzoic acid
(3,5-DABA) with 3.47 g (0.032 mol) of meta-phenylenediamine (m-PDA) in
the preparation of the monomeric polyimide precursor solution",
"preparing the dried anode intermediate after applying a coating of the
anode mixture slurry to one surface of an electrolytic copper foil to
give a thickness of 28 μm after drying", and "preparing the calcined
anode by cutting the anode intermediate into circular pieces 11 mm in
diameter which were then subjected to heat treatment (calcining) at
350° C. for 4 hr under a nitrogen atmosphere", a battery was
prepared in the same manner as for Working Example 1, and its
charging/discharging cycle characteristics were measured in the same
manner as for Working Example 1. Furthermore, the specific capacity of
the electrode surface of this lithium ion secondary battery was 6.74
mAh/cm2 (see Table 5).

[0129] The results were that the discharge capacity was 3724.5 mAh/g for
the 1st cycle, 2911.2 mAh/g for the 2nd cycle, 1860.4 mAh/g for
the 30th cycle, and 1410.8 mAh/g for the 50th cycle. In
addition, the ratio of discharge capacities (maintenance factors) for the
30th cycle vs. the 2nd cycle was
(1860.4/2911.2)×100=63.91%, and for 50th cycle vs. the
2nd cycle was (1410.8/2911.2)×100=48.46% (see Table 5).

Comparative Example 7

[0130] Except for "replacing 4.81 g (0.032 mol) of 3,5-diaminobenzoic acid
(3,5-DABA) with 3.47 g (0.032 mol) of meta-phenylenediamine (m-PDA) in
the preparation of the monomeric polyimide precursor solution",
"preparing the dried anode intermediate after applying a coating of the
anode mixture slurry to one surface of an electrolytic copper foil to
give a thickness of 31 μm after drying", and "preparing the calcined
anode by cutting the anode intermediate into circular pieces 11 mm in
diameter which were then subjected to heat treatment (calcining) at
350° C. for 4 hr under a nitrogen atmosphere", a battery was
prepared in the same manner as for Working Example 1, and its
charging/discharging cycle characteristics were measured in the same
manner as for Working Example 1. Furthermore, the specific capacity of
the electrode surface of this lithium ion secondary battery was 8.86
mAh/cm2 (see Table 5).

[0131] The results were that the discharge capacity was 3431.7 mAh/g for
the 1st cycle, 2629.7 mAh/g for the 2nd cycle, 1036.1 mAh/g for
the 30th cycle, and 746.9 mAh/g for the 50th cycle. In
addition, the ratio of discharge capacities (maintenance factors) for the
30th cycle vs. the 2nd cycle was
(1036.1/2629.7)×100=39.40%, and for 50th cycle vs. the
2nd cycle was (746.9/2629.7)×100=28.40% (see Table 5).

[0132] From the above results, the monomeric polyimide precursor solution
relating to the present invention clearly can more strongly bind the
active substance particles to the current collector body, and by
extension, along with being able to further improve the
charging/discharging cycle in a lithium ion secondary battery, can
increase the discharge capacity of a lithium ion secondary battery.

INDUSTRIAL APPLICABILITY

[0133] Since the polyimide precursor solution and polyimide precursor
relating to the present invention can be used to bind together active
substance particles and a current collector body more strongly than a
conventional polyimide precursor solution and polyimide precursor, they
are a useful binder for the active substance layer on the anode of a
lithium ion secondary battery.

[0134] In addition, along with further improving the charging/discharging
cycle of a lithium ion secondary battery compared to a convention mixture
slurry, since the mixture slurry relating to the present invention can
increase the discharge capacity of a lithium ion secondary battery or the
like, it is useful as an anode mixture slurry for forming an anode active
substance layer in nonaqueous secondary batteries such as lithium ion
secondary batteries or the like.

[0135] Furthermore, since the polyimide precursor solution and polyimide
precursor relating to the present invention are expected to exhibit good
adhesion not only for active substance particles and current collector
bodies but also toward other adherends, they can also be considered as
heat-resistant adhesive agents.

Patent applications by Hiroshi Yamada, Shiga JP

Patent applications by Takuhiro Miyuki, Osaka JP

Patent applications by Tetsuo Sakai, Osaka JP

Patent applications by I.S.T. CORPORATION

Patent applications by National Institute of Advanced Industrial Science and Technology